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National Market System

A trading system listing securities that trade in both New York and on regional exchanges. This allows investors to find the best price available for securities. The NMS also facilitates trading of certain over-the-counter stocks. It is sponsored and managed by NASDAQ and FINRA. See also: 19c-3 stock.

Normal Market Size

The number of shares in a publicly-traded company that can be traded at a given price. The normal market size is a set number determined by the stock's market capitalization. Market makers must trade within the parameters of the normal market size. If a market maker wants to buy or sell more shares than the normal market size, he/she must negotiate a new price. The normal market size exists to keep particularly large orders from affecting the share price, thus reducing volatility.


National Market System (NMS).

The National Market System (NMS) links all the major stock markets in the United States and was developed to foster competition among them.

Federal rules require these trading centers to ensure that transactions are executed at prices at least as good as protected quotations displayed at another center. A protected quotation is one that's immediately and automatically accessible.